With continuous development of communication technologies, modern mobile communications tend to increasingly provide users with multimedia services with high-speed transmission. FIG. 1 illustrates a system architecture diagram of SAE (System Architecture Evolution). As shown in FIG. 1, a UE (User Equipment) 101 is a terminal apparatus for supporting a network protocol. An E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) 102 is a radio access network comprising a base station (eNodeB/Node B) for providing the UE with interfaces to access radio network. An MME (Mobility Management Entity) 103 is responsible for managing mobility contexts, session contexts and security information of the UE. An SGW (Serving Gateway) 104 mainly provides a functionality of user plane. MME 103 and SGW 104 may be located in the same physical entity. A PGW (Packet Data Network Gateway) 105 is responsible for billing, legally interception and etc. PGW 105 and SGW 104 may also be located in the same physical entity. A PCRF (Policy charging and rules function) 106 provides QoS (Quality of Service) strategies and charging rules. An SGSN (Serving GPRS Support Node) 108 is a network node apparatus for providing data routing in a UMTS (Universal Mobile Telecommunications System). An HSS (Home Subscriber Server) 109 is a home ownership subsystem of UE and is responsible for protecting user equipment information, such as current locations of the user equipment, addresses of the service nodes, user equipment security information and packet data contexts of the user equipment.
It is known from FIG. 1 that, generally, the user equipment (UE) may establish a communication connection with an operator core network (hereinafter, abbreviated to a macro core network to distinguish it from a local core network) through a radio access network to which UE accesses. However, when the radio access network is an isolated network (i.e., there is no connection between the radio access network and the macro core network), UE accessing to the radio access network cannot communicate with the macro core network. Here, there are several conditions in which the radio access network becomes the isolated network as below: (1) a fixed base station loses a backhaul network connection with the core network and cannot be connected with the core network in the isolated state. One or more isolated and fixed base stations may constitute an isolated radio network. (2) For requirements of communication services with public safety, some nomadic base stations are deployed temporarily in some areas without macro radio network coverage in order to provide the public safety users with public safety services. These nomadic base stations generally do not have the backhaul to connect to core network entities of the macro network. One or more nomadic base stations may constitute an isolated radio network. (3) One or more isolated and fixed base stations and nomadic base stations may constitute an isolated radio network.
When the radio access network is isolated completely or the bandwidth between the radio access network and the core network is limited, it is still desired that safe and reliable services can be at least provided to the public safety UE, thereby supporting implementation with public safety tasks. At present, in order to make the isolated radio network providing the public safety public safety UE services, a local core network can be enabled for the isolated radio network. Particularly, if the fixed or nomadic base stations support functions of local core network, after the base stations become the isolated state, the local core network can be enabled to serve UE(s), to provide reliable local bearer for UE(s). Alternatively, when an isolated base station detects a local core network which is allowed to connect, for example, the local core network enabled by another base station, the isolated base station can establish connections with the detected local core network, and then provide UE with services. Generally, there is no connection between the local core network and the macro core network.
Although the isolated radio access network and the local core network can constitute an integral isolated radio network, there are also several problems in an aspect of enabling the user equipment to access the radio network.